The North Carolina election to decide on a state constitution amendment to ban same-sex unions has emotions running high at polling stations and is the "craziest in 13 years", according to a senior official at the board of elections in the state capital.

Gary Sims, the deputy director of Wake County board of elections in Raleigh, told the Guardian that there were "some really angry people" on both sides of the highly-charged debate.

Observers from the Republican party have sought to "challenge and confront" precinct officials from the board and were "clogging up the phone lines" back at Wake County headquarters. "This is the craziest election I've seen in 13 years" said Sims, at his office next to the courthouse.

"We've seen political party observers who are not precinct officials. They can ask to be observers. They want to challenge and confront and it's a problem for our precinct officials."

He said the reason for the confrontations varied, from calling up the board of elections to complain that there wasn't a chair for them to sit on to pushing officials to get people to show ID at the polls.

"They have been clogging up the phone lines and getting mad at us," said Sims. "People have to state their names and addresses and we check them. But they are challenging officials to make them show ID. They have an agenda, the ones that we've been getting trouble from."

When asked whether the trouble was coming from the groups for or against Amendment 1, Sims said: "Put it this way: we had zero Democratic party observers." He added: "I've probably said more than I should."

There were also problems with voters not being registered turning up to vote, he said. "We are seeing a very high turnout." The state has already seen record number of early voters.

The outcome of the poll on Amendment 1, which would ban same-sex marriage, civil unions and would even prevent state recognition of heterosexual domestic partnerships, is being closely monitored across America.

High profile figures, including President Barack Obama and former president Bill Clinton, who recorded telephone calls to voters, have asked them to reject the amendment. Opponents also held marches, put out television ads and gave speeches, including one by Jay Bakker, son of televangelists Jim Bakker and the late Tammy Faye Bakker.

Billy Graham, the evangelical preacher who at age 93 remains influential in the state where he has a stretch of road named after him, was featured in full-page newspaper ads supporting the amendment.

Both sides spent a combined $3m on their campaigns. The latest polls predicted the measure will pass.

Twenty-eight states have already passed a constitutional amendment defining marriage as solely between a man and a woman. However, the amendment to the North Carolina constitution goes beyond current state law, which already bans same-sex marriage, by preventing other forms of domestic unions from carrying legal status.

Lawyers and campaigners for the anti-amendment campaign have warned that this could cause a host of problems for unmarried couples, including erasing health benefits for the children of public employees in certain parts of the state. They also say it could disrupt protection orders for unmarried couples and impact victims of domestic violence.

• This article was amended on 9 May to correct a sentence that stated that the North Carolina state constitution already banned same-sex marriage. It should have said that same-sex marriage is already banned under state law.